This invention relates to an aircraft propulsion control system.
A modern commercial aircraft comprises an airframe and two or more propulsion modules attached to the airframe. Each propulsion module includes a propulsion engine, which may be a jet engine having a propeller or unducted fan, a fuel source, and electrical generators. Each engine is provided with engine condition sensors and engine control drivers. The engine condition sensors generate condition signals representative of various parameters that characterize the operating condition of the engine, whereas the engine control drivers receive command signals relating to control inputs to the engine and establish the values of those control inputs. For example, the engine condition sensors might sense the temperature and pressure at various locations in the engine, in the manner described in International Publication No. WO 84/04829 published Dec. 6, 1984 (Bluish et al), and the engine control drivers might include a fuel metering valve and a stability bleed valve. Each propulsion module also includes an engine electronic control unit which receives signals provided by the engine condition sensors and delivers them to the airframe, and receives command signals provided by the airframe and delivers them to selected engine control drivers.
Prior to the use of engine electronic control units, the pilot had quasi-direct control over some individual engine functions. For example, to issue a thrust command the pilot provided a bias to the fuel metering valve and aircraft devices also introduced a bias to the fuel metering valve as a means to coordinate the engine parameters and maintain stable engine operation. However, it was not a precise form of control as the amount of thrust actually delivered depended on altitude, Mach number, and temperature. To achieve the desired level of thrust, the pilot monitored engine parameters and manually readjusted the fuel command so that the engine parameters corresponded with a handbook lookup table.
Currently, an engine electronic control unit performs the required coordination of engine parameters. The pilot issues a thrust command to the engine electronic control unit, and the control unit establishes the desired level of thrust without further pilot input. Each engine electronic control unit has two functionally identical channels, and each channel is able to read from the engine condition sensors and write to the engine control drivers. In an aircraft having two engine propulsion modules, each engine has sufficient power to keep the aircraft airborne by itself. Therefore, a fault in one channel of one engine electronic control unit will not result in catastrophic loss of power so long as at least one of the other three channels continues to operate.
The engine electronic control unit is responsible for monitoring sensor parameters such as engine RPM, engine combustion pressure, and exhaust gas temperatures and in response to these parameters the engine electronic control unit directs engine control functions such as stability bleed and fuel metering to maintain the engine in a stable operating condition, and the pilot need only provide a thrust command. In performing these functions, the engine electronic control unit must have access to non-engine unique data including aircraft altitude, Mach number, and air temperature. In current engine electronics systems, this data is provided by dedicated electrically conductive wires running from the engine electronic control unit to the particular aircraft component providing such data. However, dedicated electrically conductive signal paths between a control unit and each aircraft component requiring communication with the control unit are undesirable because of the number of connections required and the potential for a fault in the airframe or either of the engines to follow that electrically conductive path and cause all engines to fail.
The airframe includes flight deck controls and flight deck displays. The flight deck controls include command transducers for issuing command signals to the engine electronic control units, and the flight deck displays receive the condition signals generated by the engine condition sensors and provide displays of the values represented by those signals. The flight deck controls communicate with each engine control unit by dedicated electrically conductive wires. Most of the flight deck displays may receive engine related data by way of digital data bus(es); particular flight deck displays, such as fire warning and overheat indication, may receive their data from the engine by way of separate dedicated electrically conductive wires.
Multiple engine aircraft may include apparatus for synchronizing engine RPM and/or phase in order to reduce cabin noise and structural vibration. Such apparatus normally includes an isolation station mounted on the airframe and coupled to each engine by electrically conductive signal paths. The isolation station thereby provides electrically isolated engine-to-engine communication. However, use of an electrically conductive signal path and an isolation station on the airframe to provide engine-to-engine communication is undesirable because it becomes difficult to enforce such isolation. It is not possible to guarantee that the isolation will remain because for some unanticipated reason, it is possible for a user to tie into the isolation station and violate the engine-to-engine isolation.
Because of the complexity of modern aircraft, numerous signal-carrying connections pass through connectors forming an airframe/propulsion module interface. In order to insure that the danger of connector failure will not impair the reliability of the aircraft, the signal paths of each channel are provided by way of separate connectors, and this in turn increases the number of connections. There may be several hundred electrical connections accommodated by multiple connectors. Each connector comprises an airframe part and an engine part, connected together in releasable fashion. There is always a possibility that the two parts of a connector will separate or that individual pin connections will fail resulting in interruption of the connections that should be provided by that connector. Each connection between the propulsion module and the flight deck controls or flight deck displays increases the cost of wiring, the mass of the aircraft, and the probability of fault due to connector failure.
The problem of electrical fault propagation is a paramount concern in aircraft electronic systems. Current safety practices do not allow multiple engine electronic controls to interface with or connect directly to an electrically conductive universal bus because an electrical fault, e.g. a short or an electric impulse caused, for example, by lightning, in one aircraft component can spread into other components by way of the bus.